In expectation of American landings in the Home Islands, the Yokosuka naval district began preparing close-combat Tokko frogmen units for destroying American landing craft on their approach to the beach. The Fukuryu (Crouching Dragon) were equipped with a special diving suit and breathing apparatus, of which about 1,000 were manufactured by August 1945, with a total of 8,000 planned by September 1945. The Coast Surprise Attack Force was intended to total 6,000 frogmen and to be ready for combat by October 1945.
The primary Fukuryu weapon was the Type 5 Attack Mine, which was a 22lb (10kg) explosive charge on the end of a long pole and fitted with a contact fuze. A Fukuryu defense position would start with a row of contact mines, tethered to the sea floor at a depth of 32–49ft (10–15m), which would be released by the Fukuryu frogmen to bob to the surface at the appropriate moment. Closer to shore were three rows of Fukuryu frogmen, with the rows 66yds (60m) apart and the frogmen in a line 55yds (50m) from each other. By staggering the rows, there would only be a maximum gap of 22yds (20m) for the approaching landing craft.
The intention was to deploy these forces in water about 13–20ft (4–6m) deep. The swimmers would thrust their Type 5 mines against the bottoms of landing craft as they approached overhead, hopefully sinking them. A variety of experiments were conducted to create “underwater foxholes” using concrete pipes or pre-fabricated concrete shelters to help shelter the Fukuryu frogmen from any American countermeasures, as well as to protect them from the blasts when nearby frogmen set off their lunge mines. The organization of the Fukuryu was based on a section of six frogmen, with five sections per platoon, five platoons per company, and three companies per battalion. The first Fukuryu unit was the 71st Totsugekitai Arashi (Special Attack Unit), raised in Yokosuka in the summer of 1945 with two battalions and a further four in training. Eventually, this formation was expected to deploy about 4,000 frogmen in the defense of Tokyo harbor and the invasion of the nearby Honshu beaches. The 81st Arashi at Kure and the Kawatana Arashi at Sasebo were intended to deploy 1,000 divers each. The IJN staff was very keen on the idea and wanted to deploy 40,000 frogmen for the final defense of Japan, but the plan was constrained by the lack of underwater equipment.
One of the most challenging threats facing Japanese infantry in the Pacific fighting was the widespread use of M4 medium tanks by the US Army and the US Marine Corps. The Japanese infantry lacked an effective antitank weapon comparable to the German Panzerfaust or American bazooka. A variety of weapons were hastily deployed to deal with the tank threat, including the Type 99 magnetic demolition charge, and various satchel charges that could be thrown under tanks or onto their engine decks.
US Navy personnel inspect a group of Shinyo Type 1 boats near Nagasaki in September 1945, some of the 200 assigned to the Kawatana Assault Group. (NARA)
This wartime US Navy intelligence drawing shows the configuration of the Fukuryu frogman and his underwater breathing apparatus. The inset drawing to the right shows a cross-section of the Type 5 attack mine; the upper half contains the 22lb (10kg) explosive charge, while the lower part is a hollow float chamber. Below is a silhouette drawing showing the relative size of the Fukuryu frogman with his anti-craft lunge mine. (NARA)
During the Philippines campaign in the autumn of 1944, the IJA 14th Army introduced the lunge mine. This was a shaped-charge warhead placed on the end of a long pole. The Japanese infantryman hid until a tank passed, then rushed out and pushed the mine against the tank. The impact detonated the charge, but the soldier was likely to be killed in the process. Another kamikaze tactic used in the Philippines as well as on Iwo Jima and Okinawa was the use of Nikaku “human mine” tactics, where a Japanese infantryman would carry a special back-pack mine on straps over his shoulders. He would approach the enemy tank, then throw himself between the tracks and pull a detonating cord, setting off the charge under the tank’s hull.
Although Japanese close-range antitank efforts were quite effective in the 1945 fighting, most of the American tank casualties came from more conventional tactics including the co-ordinated use of mines, antitank guns, and other types of antitank weapons. There was at least one instance of the use of kamikaze tanks. In April 1945, when US forces were approaching the IJA headquarters in Baguio on Luzon, Gen Tomoyuki Yamashita ordered a kamikaze attack by fitting large explosive charges to the front of a Type 97 medium tank and Type 95 light tank, which were then camouflaged with brush while hidden along the road. When US M4 medium tanks appeared around a bend on Route 9 on the morning of April 17, the two Japanese tanks raced forward and rammed the enemy vehicles, but the charges failed to detonate.